ABSTRACT: A study of the sulfide layer on Del Monte beach in
Monterey, California was conducted to determine the effects
that wave size, sand size, and organic content might have on
the layer. Meiofauna distributions were also examined in
relation to this darkened sand. A sulfide layer was found
to form under conditions of decreased wave action, decreased
sand size, and increased organic content. Laboratory experi¬
ments augmented these findings on sand size and organic con¬
tent, with increasing organic content increasing the dark¬
ness of the layer. Meiofaunal counts were found to drop sharp¬
ly in the sulfide layer, not only in the number of organisms,
but also in the diversity.
INTRODUCTION: During preliminary studies of several Monterey
Bay sandy beaches, it was noticed that a black sulfide layer
occurred on some beaches but not on others. Perkins (1957)
dealt with the characteristics of the layer, but made no men¬
tion of the conditions necessary for its formation. Bruce (1928)
referred to the sulfide layer as existing where the sand ap¬
peared to be of a finer grade and organic debris naturally ac¬
cumulated. An investigation was begun to determine some of the
physical parameters necessary for the formation of the sulfide
layer. Those factors studied were sand size, wave size, and
organic content of the sand.
In the laboratory effects of particle size and organic
content on the formation of the sulfide layer were studied
using both a stagnant and a percolating system. These exper¬
iments were designed to augment field observations.
During the preliminary studies a sharp decline in both
the abundance and diversity of meiofauna was found. Zobell
(1946) remarked that the bacteria in the sulfur cycle in the
sea "might yield water or mud uninhabitable to other organisms
or may be growth promoting". Hulings (1971) suggested that the
sulfide layer might be an area of enriched meiofauna. Perkins
(1958) found that within the sulfide layer the population of
nematodes was only 14.6% of the population above the layer.
In view of these discrepencies a study to examine the distri¬
bution of meiofauna within and above the sulfide layer was
included in the current study.
MATERIALS AND METHODS: The beach investigated was Del Monte
beach, protected on the west by the Monterey Harbor and break-
water while open on the east to Monterey Bay. This beach is
subjected to a gradient of wave conditions and should provide
a gradient of other physical parameters related to wave action
and of interest to this study.
At seven locations within a two mile stretch of beach,
transects were set perpendicular to the water's edge. Cores
were taken every ten feet to determine the appearance and
depth of the sulfide layer. At several intervals along these
transects sand samples were taken both in and directly above
the sulfide layer for later analysis of meiofauna concentration,
organic content, and particle size. Organic content of the
sand was determined using a wet chromate oxidation method a¬
dapted from Strickland and Parsons (1968). Particle size was
determined using a dry sifting technique with a series of
Tyler screens.
Extraction of meiofauna was accomplished using a modified
technique of Gray (1971). 500 milliliters of sand were washed
five times with approximately 750 ml of 6% MgClo solution,
followed by two rinses with 750 ml of 60°C seawater. Counts
were converted to organisms per liter of sand. Meiofaunal
contributions from the seawater were found to be negligible.
The method proved to yield 90% of the animals obtained by ex¬
haustive extraction.
-4-
RESULTS: A diagram of the area of study is presented in Figure
1, which includes descriptive information. Wave size generally
increases along the shore from transect 1 to transect 7. The
sand throughout this stretch of beach was well sorted and par¬
ticle size did not differ appreciably within transects. Av¬
erage particle size increased,however, with increasing distance
from Pier +2. The organic content of the sand along each tran¬
sect was patchy. Average organic content appeared to decrease
with increasing distance from the pier. The organic content
of the darkened sulfide layer was generally higher than that
of the sand above it. On transects 1 through 4, a darkened
sulfide layer was found while on transects 5 through 7, the
sulfide layer was not present. In general, from transect 4
to transect 1, the sulfide layer increased in darkness. No
relationship was found between tidal level and degree of dark¬
ening. It was noted, however, that the layer was generally
darker with increasing depth into the sand.
To determine the topography of the sulfide layer, a study
of a 400 square foot area adjacent to Pier +2, see Figure 1,
was undertaken. Lines and levels were used and measurements
of the depth of the sulfide layer were made at two foot inter¬
vals. The results were then plotted as depth below a reference
point equivalent to the highest point in the study area, and as
depth below the surface of the sand. Depth below the surface
varied from 5 to 25 cm and showed no definite relationship
to the surface topography of the sand.
To test the effect of particle size and organic content on
the formation of the sulfide layer, a series of glass 500, 1000,
and 2000 ml cylinders were prepared to simulate field conditions.
Three grades of sand were used singly and in a mixture. Fine
sand corresponded to a particle size passing .250mm and caught
by .125mm screens, medium sand passed .500mm and was caught by
.25Omm screens, coarse sand passed 2.00mm and was caught by
50Omm screens, and mixture was a combination of equal weights
of fine, medium, and coarse sand. Sodium acetate in seawater
solution was used to vary the organic content of these pre¬
parations. The concentrations of sodium acetate used were
1.0%, 0.5%, 0.25%, 0.1%, 0.05%, 0.025%, and 0.0%. As an in¬
dicator of the production of HoS, ferrous sulfate was added
to a concentration of 0.02%. No effect related to cylinder
volume was observed.
The cylinders were filled to a height of 40 cm, mixed
with a seawater solution by repeated inversion, allowed to
settle, and maintained close to 13°C in total darkness to
prevent the growth of photosynthetic organisms. They were
inspected at intervals and rated as to color.
In addition, sulfide formation in a percolation unit was
studied. An apparatus modeled after Kaufman (1966) was con-
structed from clear plastic tubing with an inside diameter
of 7.5 cm and 60 cm in length. The column was filled to a
height of 50 cm with fine sand. The rate of percolation was
maintained close to 10 ml per minute. The rate of supply of
solution was 15 ml per minute, thereby creating an overflow
and a constant head of 10 cm. The solution was recycled from
a five gallon reservoir. Sodium acetate in seawater at concen¬
trations of 0.1%, and 0.05% were used as well as seawater with¬
out additions. The contents of the reservoirs were changed
every twelve hours.
In the stagnant system of cylinders, the darkened sand
appeared first as a myriad of small darkened areas which later
merged together to provide a more homogeneous darkening. The
entire cylinder darkened and never was a layer of undarkened
sand found in the stagnant cylinders. The minimum incubation
period required for noticeable darkening was five days. Gen¬
erally, the cylinders with higher concentrations of sodium ac¬
etate solution darkened most rapidly and were of a darker color
after fifteen days of incubation. In solutions of concentra¬
tions of 0.1% and above, the fine and mixed sands were darker
after fifteen days than were the coarse and medium sands. There
appeared to be no overall relationship between the original or-
ganic content of the sand and the degree of darkening.
In the percolation system, greater concentrations of sodi¬
um acetate solution in seawater again gave rise to an increased
rate of formation of the sulfide layer. The minimum period for
a noticeable degree of darkening was seven days. In contrast
to the stagnant system, at concentrations of 0.1% and 0.05%
sodium acetate solution in the percolation unit, darkening
began ten om below the sand surface. After ten days, however,
this ten centimeters of white sand also began to darken. The
concentrations of 0.1% and 0.05% sodium acetate resulted in a
black sand in the percolation system while these same concen¬
trations in the stagnant system resulted in medium gray and
light-medium gray. After fifteen days the 0.0% unit had not
darkened. During formation, the layer increased in darkness
with increasing depth, but at the end of fifteen days the
column was a solid black. These experiments are summarized
in Table 1.
Variation in counts of meiofauna was large. See Table 2.
There appears to be an increase in the number of species with
increasing tidal height. The peak occurs at a tidal height of
+6 to +7 feet for the sand above the layer, and at +3 to +4
feet for the sulfide layer. Nematodes were the most wide¬
spread animals both above the sulfide layer, with their peak
being at +4 to +5 feet, and within the layer, with their peak
occurring at 0 to +1 foot in tidal height. Harpacticoid
copepods, collembolids, nereid, juvenile and adult archiannelid
and gpionid annelids were never found in the sulfide layer.
DISCUSSION: Of the three physical parameters studied, it is
felt that wave action is the most important factor governing
formation of a sulfide layer. Wave action affects particle
size, and these two factors in turn can greatly influence the
organic content. Mild wave action can deposit a finer grade
of sand and can allow a greater proportion of the suspended
organic material to settle, whereas, heavy wave action, through
greater turbulence, maintains fine sand and organic material
-8-
in suspension. The finer grade of sand can also contribute
to increased organic content by sieve-like trapping of organic
material. A mixture of sand should also produce a fine sieve
through the filling of large pores with the smaller sand part¬
icles.
The presence and darkness of a sulfide layer on Del Monte
beach increases with decreasing wave action, decreasing particle
size, and increasing organic content. The laboratory experi¬
ments using cylinders also show an increase in darkening with
increasing organic content, especially in a fine grade or mix¬
ture of sand. The final degree of darkening of a sulfide layer
could be dependent upon the available supply of organic mater¬
ial and length of time it stays in deposits. The difference
in coloration between the stagnant cylinders and the percolation
tubes at the same concentration of sodium acetate is probably
due to the extended maintenance of required organic material
as sodium acetate in the percolation system.
Although on Del Monte beach the darkened layer was found
only in areas of finer sand, the coarse particles in the stag¬
nant cylinders also gave rise to darkened sand. The differ¬
ence in these observations may be explained by the stagnancy
of the cylinders as opposed to the instability of a sandy beach.
In the laboratory, the stagnant system required at least five
days of incubation before a sulfide layer appeared. On a
sandy beach, where erosion and deposition of sediments may
occur constantly, accumulation of organic material is inhibited
and anaerobic bacteria may be exposed to oxygen often enough
to prevent formation of a darkened sulfide layer. Thompson
(W.C. Thompson, personal communication) has examined the same
stretch of beach chosen for this study for several years. His
observations indicate there is a greater amount of deposition
and erosion with increasing distance from Pier #2. This could
explain the absence of a sulfide layer in transects 5, 6, and 7.
The meiofaunal counts definitely disagree with the pro¬
position that the sulfide layer may be rich in meiofauna. On
the average, the layer was found to contain only 11% of the
number of organisms in the sand above and only 40% of the
classes. This does not vary greatly with the nematode counts
of Perkins (1958) who found in the sulfide layer only 14.6%
of that above. In two cases, counts of Platyhelminthe from the
darkened sand exceeded counts of the sand directly above,
which may be due to a preference, found by Sterrer (1971),
of gnathostomulids for the HoS-rich sand. Perkins (1958)
and Sterrer (1971) both suggest that the meiofauna found in
the layer may be feeding on the bacteria. The sharp decrease
in numbers in the layer shows that the distribution of meiofauna
is affected by some property of the sulfide layer. Polluck
(1971) showed that in several cases meiofaunal distributions
were limited by a lack of oxygen. The presence of HyS in sand
is usually associated with a diminishing supply of oxygen and
may be the limiting factor in distribution. Further invest¬
igation of the actual limiting factor should prove interesting
and further elucidate the affect of sulfide-rich sands on the
sandy beach ecosystem.
LITERATURE CITED
Bruce,J. Ronald. 1928. Physical factors on the sandy beach.
Part II. Chemical changes- carbon dioxide concentration
and sulfides. J. Mar. Biol. Ass.,U.K., 15: p.559.
John S. 1971. Sample size and sample frequency in re¬
Gray
lation to the quantitative sampling of sand meiofauna,
p.192. In Hulings, N.C.(ed), Proceedings of the First
International Conference on Meiofauna. Smith. Cont.
Zoo., 76.
Hulings, N.C. and J. S. Gray (eds). 1971. A manual for the
study of meiofauna. Smith. Cont. Zoo., 78:p.7.
Kaufman, D.D. 1966. An inexpensive, positive pressure, soil
perfusion system. Weeds 14: 90-91.
The blackened sulphide- containing layer
Perkins, E. J. 1957.
of marine soils with special reference to that found at
Whitstable, Kent. Ann. Mag. Nat. Hist.,ser.12,10: 25-35.
Perkins, E. J. 1958.
The food relationships of the microbenthos,
with particular reference to that found at Whitstablé, Kent.
Ann. Mag. Nat. Hist.,ser.13,1: 64-7
Polluck, L. W. 1971. Ecology of intertidal meiobenthos, 141¬
145. In Hulings, N.C.(ed), Proceedings of the First
International Conference on Meiofauna. Smith. Cont.
Zoo.,76.
Sterrer, W. 1971. Gnathostomulida: problems and procedures,
9-14. In Hulings, N.C. (ed), Proceedings of the First
International Conference on Meiofauna. Smith. Cont.
Zoo.,76.
ACKNOWLEDGMENTS: We wish to thank the entire faculty and staff
of Hopkins Marine Station for their assistance. We especially
wish to thank Dr. John H. Phillips, without whose enthusiasm,
advice, and time, this study would never have been attempted
or completed.
Figure 1. A map of the area studied showing associated phy¬
sical parameters and distribution of the darkened
sulfide layer.
MONTEREY BAY
Marina
Pier No. 2
H
scale in feet L
L
L
TRANSECT NUMBER
COLOR OF SULFIDE LAYER
OBlac
Dark
Light
Black
AT 0,3,6 FEET ABOVE
3Black
Dark
Light
Dar
MEAN LOWER LOW
Black
Dark
Black
Blac
WATER
118
077
130
146
134
SAND SIZE-AVG. MD %
ESTIMATED WAVE SIZE
10
0.5
0.5
2.0
0.5
IN FEET, APRIL 26, 1972.
Lg CARBON/gm dry wt sand
587
348
355
346
ABOVE SULFIDE LAYER
885
555
408
847
IN SULFIDE LAYER
598
616
571
343
382
AVERAGE
0.70
3.0
400
4.0
0.60
4.0
443
1
Table 1.
Experimental results of the construction of a dark¬
ened sulfide layer in both a stagnant and a per¬
colation system.
LEGEND
(For Table 1.)
Sodium acetate refers to % concentration of sodium acetate in
seawater.
Sediment size refers to the diameter of the sand particles
Fine: 0.125 - 0.250 mm
used:
Med: 0.250 - 0.500 mm
Coarse: 0.500 - 2.00 mm
Mix: a mixture of equal weights of fine, medium,
and coarse sand.
Organic content refers to micrograms of carbon in the oxidation
state of glucose per gram of dry sand.
No change, light gray, etc. refer to the color of the sand.
Numbers in the bars below no change, light gray, etc. refer
to days of incubation.
SODIUM
SEDIMEN
ACETATE
SIZE
ine
0
10
med
coarse
10
0
mix
fine
0.9
med
105
coarse
015
O5
mix
025
Ifine
med
0.25
coarse
0.25
025
mix
10
Ifine
med
TOI
01
coarse
O
mix
fine
005
OO5
med
coorse
0.05
0.0
mix
0025
Ifine
9.025
med
0025
coarse
0025
mix
00
fine
med
HOO
00
coorse
mix
O0
—00
fine
med
00
00
coarse
mix
00
PERCOLATION
O.1
fine
OOE
Tine
0C
fine
ORGANIC
CONTEN
1600900
500600
600900
600-900
600900
B00-60
600-90(
60090
60090
30060
60090
6009
300-600
3007600
0060
30060
30060
300600
30060
300600
30060
300600
30060
300600
booso
300600
510
00900
5/015
300600
30060
5,015
300600
5,05
30060
5/0,5
100600 51015
300600
30060
00600
501
CHANGI
LIGHI
GRAT
10,15
105
0E
10.
05
LICHEMEO
GRAY
MEDIUM
GRA
DARK
GRA
B140K
1115
7486
1
Table 2. Diversity and distribution of meiofauna both in and
above the sulfide layer.
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